﻿//
// Created by francklinson on 2021/3/17.
//

#include <iostream>
#include <string>

using namespace std;

string version1(const string &s1, const string &s2);

const string &version2(string &s1, const string &s2); // has side effect
const string &version3(string &s1, const string &s2); // bad design

int main()
{
    string input;
    string copy;
    string result;

    cout << "Enter a string: ";
    getline(cin, input);
    copy = input;
    cout << "Your string as entered: " << input << endl;
    result = version1(input, "***");
    cout << "Your string enhanced: " << result << endl;
    cout << "Your original string: " << input << endl;

    result = version2(input, "###");
    cout << "Your string enhanced: " << result << endl;
    cout << "Your original string: " << input << endl;

    cout << "Resetting original string.\n";
    input = copy;
    result = version3(input, "@@@");
    cout << "Your string enhanced: " << result << endl;
    cout << "Your original string: " << input << endl;

    return 0;
}

string version1(const string &s1, const string &s2)
{
    string temp;

    temp = s2 + s1 + s2;
    return temp;
}

const string &version2(string &s1, const string &s2) // has side effect
{
    s1 = s2 + s1 + s2;
// safe to return reference passed to function
    return s1;
}

const string &version3(string &s1, const string &s2) // bad design
{
    string temp;

    temp = s2 + s1 + s2;
// unsafe to return reference to local variable
    return temp;  // 返回局部变量的引用 不可行  内存在函数结束后被释放 不能再引用
}